New Zealand Gazette – 1876 – No. 18

Page 232

✨ Longitude Determination Report

232

THE NEW ZEALAND GAZETTE.

The chronometric difference between Garden Island (Sydney) Observing Station and the
Cathedral, Wellington, determined by Captain Nares, of H.M.S. Challenger, is
+1h. 34m. 15s. 47. Hence we have, —

	H. M. s.
Longitude of Sydney Observatory...	10 4 50.61 E.
Correction to Garden Island Station	+5.73
Cathedral, Wellington, East of Garden Island	+1 34 15.47
Correction to Wellington Observatory	-2.01
Nares's longitude of Wellington Observatory	11 39 9.80 E.

This differs nearly four seconds from Stokes's result, but Captain Nares admits that in all
probability Stokes's is the more trustworthy of the two, as in the Challenger's case
twenty-one days elapsed between the time observations at Sydney and those at New
Zealand, while the interval in Stokes's case was probably much shorter.

Separate determination of absolute longitude by transits of the moon which were made in
1869-70-71 at Rockyside, Dunedin, by Messrs. Thomson and McKerrow, and at the
Hutt, Wellington, by Mr. Jackson, were combined in 1871, by determining telegraphically
the difference of longitude between those points, with the following mean result :—

	H. M. s.
Longitude of Hutt Observatory	11 39 50.72 E.
Correction to Wellington Observatory	-35.41
Thomson and Jackson's longitude of Wel-
lington Observatory	11 39 15.31 E.

But the errors of the moon's tabular place were not taken into account in this determi-
nation. The average of these errors for the days in which the moon was observed at
Rockyside and the Hutt was about + 0s. 25, which would probably cause an error of
between +6s. and +7s. in the resulting longitude. Therefore Messrs. Thomson's and
Jackson's corrected longitude of the observatory may be taken approximately as
11h. 39m. 9s. E.

The chart longitude of Pipitea Point, in which New Zealand mean time (i.e., the time in
longitude 11h. 30m. E) is at present founded, is 11h. 39m. 11s. 53 E, so that we have,—

	H. M. s.
Chart longitude of Pipitea Point	11 39 11.53 E.
Correction to Wellington Observatory	-2.88
Present adopted longitude of Wellington
Observatory	11 39 8.65 E.

Recapitulating these five results, we have for the longitude of Wellington Observatory, as
variously determined, —

	H. M. s.
1. Palmer's absolute longitude, approximate only	11 39 4.81 E.
2. Stokes's chronometric, depending on Mel-
bourne	11 39 5.89 "
3. Nares's chronometric, depending on Mel-
bourne	11 39 9.80 "
4. Thomson and Jackson's, approximate abso-
lute...	11 39 9.00 "
5. Present adopted longitude for New Zealand
mean time	11 39 8.65 "

The mean of these is 11h. 39m. 7.63s., or within about one second of that at present adopted as the
standard for colonial time. I therefore should not recommend that any immediate change of that
standard be made. It will be soon enough to alter it once for all when the whole of the Burnham
observations have been correctly reduced and communicated to the Colonial Government, and when, by
means of the projected submarine cable, a telegraphic longitude-difference shall have been obtained
between New Zealand and the Sydney or Melbourne Observatory.

Latitude of Burnham.

The latitude of the transit-pier at Burnham, as derived from fifty-three circummeridianal
observations of north and south stars, is 43° 36′ 48″.4 south.

The Hon. the Colonial Secretary, New Zealand.